1. Field of the Invention
The field of the invention is that of the recognition of sequences of multidimensional signals, and notably sequences of image signals.
The term "multidimensional signals" is understood to mean the signals constituted by multidimensional elements or vectors. In the case of image signals, each image is a signal vector.
The invention can be applied, for example, to the automatic detection of a given sub-sequence of images in a sequence of images broadcast by a video program, enabling automatic control of selective recording operations. It can also be used as a device for obtaining access to the memory of a bank of images through the contents.
The invention can also find many applications in the fields of image processing and automatic vision, for example in robotics.
More generally, the invention can be applied to the recognition of all types of multidimensional signals, such as the time-frequency spectra of acoustic signals, radar signals or multisensor signals.
2. Description of the Prior Art
There are many known methods for the detection of a signal sequence of which there is a priori knowledge. The most commonly used technique is that of linear filtering, or of correlation according to a given standard. More precisely, when the detection does not take account of the properties of invariance, notably in rotation and in scale, the appropriate filtering technique is the one most commonly used in signal processing.
However, when the signal to be analyzed is crammed with information, for example in the case of video images, corresponding to vectors with large dimensions, the direct application of the linear filtering technique is very costly in computing time. Furthermore, the memory necessary to save the characteristics of the filter is substantial in this case.
A simpler method, in terms of the criteria of computing complexity and memory size needed, consists in carrying out a compression of the signal vector to be analyzed, before filtering. This compression has to be simple, in order to enable real-time processing. Thus, in the case of a high-definition image, it is possible to define sub-images with low resolution, of some tens by some tens of pixels, for example by taking averages of values within groups of pixels of the high-definition image.
This transformation, which is independent of the initial vector, inevitably results in a loss of information and, hence, in a loss of discrimination.
This drawback can be overcome by the simultaneous filtration, or correlation, of several vectors of the analyzed sequence. However, this leads to a major increase in the requisite computing power and memory size.
The invention is aimed at overcoming these drawbacks.
More precisely, the invention is aimed at providing a device for the recognition of sequences of multidimensional signals having high performance qualities of discrimination.
A complementary aim of the invention is to provide a device such as this, requiring filtering or correlation means of low complexity, notably as regards computing power and memory size.
Another aim of the invention is to provide a device such as this that costs little and can therefore be applied to products for mass consumption.
Another aim of the invention is to provide a device such as this that is easily programmable, i.e. a device that enables the swift modification of the sequence or sequences to be recognized.